1. Field of the Invention
The present invention relates to a method of producing tin, which is emitting the low alpha radiation by using a vacuum refining. More particularly, the impurities, such as a lead and a bismuth in the tin ore, which are the major sources of emitting the alpha radiation caused to incur the software errors in the electronic devices are removed as much as possible by utilizing the different vapor pressure of each element. So that, the emission of the alpha radiation will be minimized to prevent the occurrence of the software errors.
2. Related Prior Art
Generally, the Tin (Sn) is the main component of the soldering (main material of the solder). It is widely used for manufacturing the semiconductor component; and for connecting the semiconductor chip to the substrate; for bonding the silicon (S chip, such as a IC or LSI, to the lead frame or the ceramic package; and for forming the bump or using the wiring materials to produce the TAB (Tape Automated Bonding) or the Flip Chip.
Meanwhile, the European Union as of Jun. 1, 2006 has established the Restriction of Hazardous Substances Directive (WEEE; Waste Electrical and Electronic Equipment) and the Disposal of Electrical and Electronic Equipment (RoHS; Restriction of Hazardous Substances). The regulation has executed to prohibit the lead used in the electronic devices. Due to impact of this regulation, most of the electronic products have manufactured by using un-lead solder, which has not contained the impurities, such as a lead.
In addition, the tin as a raw material is recently used for the semiconductor component to be high-density and high-capacity. Because the tin placed near by the semiconductor chips and emitted large amount of alpha radiation, it causes a risk to loss the information in the memory cells incurring the software error (Soft error).
Generally, the crude tin emits alpha particles in a range of 2˜5 counts/cm2 hr, whereas the purified tin emits alpha particles in a range of low alpha radiation below 0.5 counts/cm2 hr, preferably below 0.02 counts/cm2 hr, more preferably below 0.001 counts/cm2 hr.
The soft error occurs due to existence of the isotopes, such as a lead and bismuth in a tin or solder. In general, the industrial tin has contained the impurity elements (210Pb, 210Bi, 210Po, etc.), which is a kind of radiation emitting the high-energy alpha particles.
Relating to this fact, the IBM has discovered in 20 years ago that the 201Pb has a decay chain. As a result, it has verified that the emission of the alpha particle of about 5.4 MeV caused to occurrence of the software errors.
In other words, as shown in FIG. 1, the half-life of 210Pb is 22.3 years via beta decay of 210Bi, 210Po converted to 206Pb. When the 210Po decays to 206Pb, it will emit the alpha particle of about 5.6 MeV.
For an example, when the high-energy alpha radiation irradiates the data stored in the memory component or recording device, it causes to disturb the data in a semiconductor device to occur the software errors. The charge energy is strong enough to convert the digital signal “0 to 1” or “1 to 0” in the recording devices or the memory component, it will be a serious problem.
As a result, a highly purified tin is required as the main material of soldering the semiconductor component. Especially, it is required the tin, which is emitted the lower alpha radiation.
For instance, the conventional technology has disclosed for manufacturing the tin, which emits the low alpha radiation in Japanese Patent Registered No. 2754030, Japanese Patent H11-343590 and Japanese Patent H01-283398.
In other words, the Japanese Patent Registration No. 2754030 disclosed, “a method for producing the highly purified tin.” It has disclosed that the highly-purifying solution of a sulfuric acid or hydrochloric acid, such as a super sulfuric acid or hydrochloric acid is used as the electrolyte, and the highly-purified tin is used as an anode for electrolysis. It has also disclosed the technology to obtain the purified tin as of the low concentrated lead, which has the alpha (α) lay as low level of counting number of 0.005 cph/cm2.
In addition, the Japanese Patent No. H11-343590 related to the technology of “method of producing the high-purity tin” disclosed that an aqueous solution contained the crude metal tin is added the acetic acid to heat, and precipitating the meta-tartaric acid, then filtered. After washing this meta-tartaric acid, it will be dissolved in the hydrochloric acid or hydrofluoric acid, then the metal tin of over 5N is extracted from the dissolution solution as the electrolyte by the electrolysis.
Further, the Japanese Patent No. H01-283398 related to the technology of “Tin and its manufacturing method” disclosed that the super sulfuric acid is used as a reagent for the electrolytic to obtain the tin, which has more than 99.99% of purity and the level of a radiation particle counting number about 0.03 cph/cm2.